The Jury's Still Out On Home Radon Risk

September 17, 1994|By Warren E. Leary, New York Times News Service.

WASHINGTON — Several new studies of radon, the radioactive gas known to cause cancer and found to be seeping into millions of homes across the country, have uncovered little evidence linking household exposure to disease, raising questions about how much risk radon poses to humans at very low levels.

Researchers say that in most cases these studies have failed to show an association between lung cancer and household radon levels at or even slightly higher than the level at which the Environmental Protection Agency recommends taking corrective measures.

The continued lack of evidence of a significant risk from radon at these levels raises questions about how aggressively the nation should try to lower radon levels in homes and buildings. The ultimate cost to meet the EPA standard is estimated at $50 billion or more, critics say.

But the EPA and other scientists contend there is enough indirect evidence that radon is a major cause of cancer at levels found in many homes to take action. The design and limited number of participants in some of the new studies fail to give them sufficient power to assess the true risks, they say.

The better-safe-than-sorry approach has many adherents. In Illinois, the Residential Real Property Disclosure Act, which goes into effect on Oct. 1, requires home sellers to disclose any known radon risk.

Radon is an odorless, colorless gas that arises naturally from the ground because of the decay of radioactive elements commonly found in rocks and many types of soil.

In a chain of radioactive decay, uranium produces radium, which gives off radon, which in turn produces radioactive breakdown products that are harmful if inhaled.

Almost all scientists agree that prolonged exposure to high levels of radon is hazardous. But uncertainty remains about the risks of low-level exposure.

Worldwide studies of lung cancer in underground miners, backed by animal research, show that long-term exposure to high levels of radon and its breakdown products causes lung cancer. The effect is heightened by cigarette smoking, researchers say.

Most radon experts concur that studies show radon gas is a genuine cancer hazard to humans at levels two to four times and above the EPA "action level" for home exposure. That level is four pico curies per liter of air or higher. A pico curie is one-trillionth of a curie, a unit of radioactivity.

According to EPA surveys, the average radon level in American homes is 1.25 pico curies, and 6 percent of all homes, or about six million, have levels of 4 pico curies or above.

But several long-awaited studies designed to quantify the radon risk in homes have not found a significant cause-effect relationship at typical levels of exposure.

Dr. Jay H. Lubin, an epidemiologist with the National Cancer Institute who has analyzed numerous radon studies, including the newest ones, said all had weaknesses that make it impossible to determine the exact risk of radon in homes.

"Evidence showing an excess risk from indoor exposure to radon remains inconclusive," he said. "The results of most of these studies is consistent with there being no effect at low levels, but there is still reason to think radon in homes is deleterious."

The data on miners are decisive in showing that radioactive particles from the decay of radon causes lung cancer, Lubin said. There is no evidence of a threshold below which any exposure would not increase risk. However, he said, differences in the environments of underground mines and homes could greatly affect actual exposures to radon, making extrapolating risks from radon in mines to houses difficult.

Based on the miner data, indoor radon exposure is estimated to be responsible for about 10 percent of the 150,000 lung cancer deaths that occur in the United States each year.

In one of the recent studies, researchers at Health Canada's Health Protection Branch looked at 738 lung cancer cases in Winnipeg and an equal number of people with similar characteristics who had not developed lung cancer. They found no increase in risk attributed to cumulative radon exposure among long-term residents.

The researchers, including Dr. Ernest G. Letourneau and Dr. Daniel Krewski, chose Winnipeg because it had the highest indoor radon levels of 18 Canadian cities surveyed. The study, published last month in The American Journal of Epidemiology, said the mean household exposure was 3.5 pico curies per liter and measurements in the basements averaged 4.5 pico curies.

Krewski said a strength of the Canadian study was to try to pinpoint total exposure by measuring radon levels in every home each person in the study had lived in; many other studies have measured radon in only one residence. Although researchers took measurements in 4,448 homes, more than a third of the eligible homes could not be tested.